Suspended body flow meters have been used since the middle of the last century for determining volume and mass flows in closed pipelines. Even today they can be found in approximately every fifth flow meter in the chemical and materials processing industry.
A suspended body flow meter, in its simplest form, consists of a conical measuring tube and the suspended body. The measuring tube is a conical tube expanding upward through which the liquid or gas flow to be measured flows upward, in which tube the suspended body, an appropriately shaped, vertically freely movable measuring element, is located, which, together with the measuring tube, forms a restrictor. The density of the suspended body is greater than that of the flowing medium. Depending on the flow, the suspended body adjusts itself in the steady state at a specific level position in the measuring tube, which results from the equilibrium of the hydrodynamic force acting on the suspended body, caused by the flow, and the difference of the weight and buoyancy forces of the suspended body. This level position is either read by the observer directly via a scale on a glass measuring tube or transferred by a magnetic coupling to an external scale and/or an electric sensor. The suspended body flow meter under consideration is such a meter in which the level position of the suspended body can be transferred by means of a magnetic coupling via an external follower magnet to a scale located in the meter housing and/or an electric sensor also located in the meter housing.
In addition to the designs with conical measuring tube and spherical or sharp-edged suspended bodies, straight measuring tubes with a measuring orifice and a conical suspended body within the orifice opening can be used. Also it is conceivable not to arrange the measuring tube vertically, in this case it being necessary to replace the weight force of the suspended body with the spring force of a spring acting on the suspended body.
The invention under consideration essentially concerns the design of the meter housing which holds at least the follower magnet and the display device converting the motion of the follower magnet, which is independent of the variation possibilities described in the case of the design of a suspended body flow meter. The second teaching of the invention here takes account of the possibility that, in the case of measurement tubes already incorporated into closed pipelines, there is the possibility of backfitting only the meter housing if necessary.
The known meter housings used in connection with suspended body flow meters for flowing media are all designed in such a way that additional mechanical and/or electrical functional units can only be connected with either the meter housing itself via screw connections or a bearing bushing of the pointer shaft bearing the pointer or the pointer shaft itself via push-on or screw connections. In the first place, it should be mentioned that suspended body flow meters are regularly supplied only in one basic design, therefore perhaps without a transmitter converting the motions of the follower magnet into electric signals or without a threshold value display arrangement mechanically displaying or electrically outputting the reaching of a minimum or maximum range of the suspended body. In the case of backfitting this suspended body flow meter with further functional units, the known methods of attachment entail problems, since they are difficult to carry out depending on the position of the suspended body flow meter and, in particular, they require increased caution in the connection with the pointer shaft.
A particular problem results from the fact that in a number of suspended body flow meters it is usual to mount on the pointer shaft a counteraeight or calibration weight with a center of gravity outside of the pointer axis for calibrating the suspended body flow meter, the position of which is determined individually in a calibration process for each suspended body flow meter. Now in order to mount the threshold value pointer arrangement with a possibly associated electrical contactor onto the bearing bushing for the pointer shaft and the associated actuating lugs on the pointer shaft itself, in the case of this suspended body flow meter, the counterweight or calibration weight must be removed from the pointer shaft. Thus, the backfitting of this known suspended body flow meter requires that then the suspended body flow meter concerned is subjected to recalibration for determining the position of the counterweight or calibration weight. This is very problematical for various reasons. First, the suspended body flow meter has to be removed from the pipeline system of the plant for calibration, which, as a rule, requires an interruption of the production process. In the second place, the calibration requires trained special personnel, which are not available at every plant, and, in addition, increased costs if they are available. Finally, in the third place, it is problematical that the necessary calibration only is to be performed by means of a calibrating device for adjusting a known flow through the suspended body flow meter. Of course, providing such a calibrating device entails considerable costs.